The following description of the background of the invention is provided to aid in understanding the claimed invention, but it is not admitted to constitute or describe prior art to the claimed invention and should in no way be construed as limiting the claimed invention.
Chitin, the chemical structure of which is shown in FIG. 1, is the main constituent in the shells of crustaceans and is the most abundant naturally occurring biopolymer other than cellulose. Chitosan, the chemical structure of which is also shown in FIG. 1, is derived from chitin and can be formed by deacetylation of chitin. Chitosan is commercially available in a wide variety of molecular weights (i.e., 10-1,000 kDa) and usually has a degree of deacetylation ranging between 70% and 90%.
Chitosan has been reported to form compositions with a variety of anionic drugs and polyanions such as indomethacin, polyacrylate, pectin, acacia, alginate, hyaluronate, and some polysaccharides (J. Kristl et al., Hydrocolloids and Gels of Chitosan as Drug Carriers. Int. J. Pharm., 99; 13-19 (1993); S. Shiraishi et al., Controlled Release of Indomethacin by Chitosan-Polyelectrolyte Complex: Optimization and In Vivo/In Vitro Evaluation. J. Contr. Rel., 25; 217-225(1993); M. M. Meshali and K. E. Gabr. Effect of Interpolymer Complex Formation of Chitosan with Pectin or Acacia on the Release Behavior of Chlorpromazine HCl. Int. J. Pharm., 89; 177-181(1993); T. Nagai et al., Application of Chitin and Chitosan to Pharmaceutical Preparations. In: "Chitin, Chitosan, and Related Enzymes." Academic Press, New York, 1984, 21-39; H. E. Rios et al., Counterion Binding to Cationic Polyelectrolytes in Aqueous Solution. J. Polym. Sci., Polym. Phys. 29; 805-809(1991); T. Takahashi et al., Characteristics of Polyion Complexes of Chitosan with Sodium Alginate and Sodium Polyacrylate. Int. J. Pharm., 61; 35-41(1990); K. Takayama et al., Effect of Interpolymer Complex Formation on Bioadhesive Property and Drug Release Phenomenon of Compressed Tablets Consisting of Chitosan and Sodium Hyaluronate. Chem. Pharm. Bull., 38; 1993-1997(1990); R. Srinivasan and R. Kamalam. Polyelectrolyte Complexes of Glycol-Chitosan with Some Polysaccharides. I. Mixing Ratio and Dielectric Properties. Biopolymers, 21; 251-263(1982).
These polyelectrolyte compositions with chitosan have been well characterized in terms of optimal complexation conditions (i.e., ionic strength, pH, temperature, and ratios of components), composition morphology, and composition stability. Chitosan has also been proposed for use as a biomedical membrane, artificial skin, for delivery of anti-cancer drugs to tumor cells, and as a pharmaceutical delivery system for prescription drugs. In addition, chitosan has been shown to be biodegradable, biocompatible, to have very low toxicity, and no thrombogenic activity.
The use of chitosan as a component of a complex in a non-viral gene delivery system in an in vitro use is described in Mumper et al., Proceed. Intern. Symp. Control. Rel. Bioact. Mater., 22:178-179, 1995, incorporated herein by reference in its entirety, including any drawings and figures. Chitosan is described as effective in condensing negatively charged plasmid DNA due to charge interactions with the positively charged chitosan. Mumper et al., report on the correlation between physicochemical properties of the gene transfer complexes and their in-vitro transfection efficiency. Specifically, they report that the use of smaller molecular weight chitosan as a component of the delivery system (i.e., chitosan in the range of 2-4 kDa M.W.) results in the smallest particle of the gene delivery system and also in an increased transfection of cells with the condensed delivery system.
Chitosan has also been used with a pharmacologically active compound such as insulin in the form of a solution or as a coating on polystyrene microspheres. These formulations involved the use of chitosan of molecular weights of 10,000 or greater, preferably at least 100,000 or 200,000 and most preferably about 500,000. The chitosan/insulin formulations were prepared by mixing equal volumes of insulin and chitosan in solution. The formulation was administered nasally to rats via microsyringe. These formulations have been reported as disclosed in WO 90/09780.
The use of chitosan in microspheres containing naked DNA has been reported by Alexakis et al., Applied Biochemistry and Biotechnology, 50:93-106, 1995, incorporated herein by reference in its entirety, including any drawings and figures. The immobilized DNA within chitosan-coated alginate microspheres was designed to test the role of metabolic byproducts of digestion in promoting damage to DNA. The microspheres were designed to pass through the digestive system without being taken up by cells in the animal. Upon excretion, the intact microsphere can be recovered and the DNA examined to asses the role of metabolic byproducts of digestion in promoting cancer through damage to nucleic acid. The microspheres were designed to retain the DNA within their core during transit through the animal. The microsphere prevented access to DNA from hydrolytic enzymes but allowed metabolic byproducts of digestion to cross or exit the microsphere shell. The reported recovery rate of the microspheres after administration was 97%. According to the abstract, leakage of DNA from intact microspheres was not observed.